Contact material

ABSTRACT

SILVER-ZINC SOLID SOLUTION ALLOYS USED FOR CONTACT MATERIALS HAVE THE DISADVANTAGE THAT THEY FORM ZINC OXIDE IN AN OXIDIZING ATMOSPHERE. THIS DISADVANTAGE IS OBVIATED BY ADDING ALUMINUM TO THE SOLID SOLUTION. THE ATOM PERCENTAGES OF ZINC AND ALUMINUM ARE 5 TO 36% AND 0.5 TO 5% RESPECTIVELY, THE REMAINDER BEING SILVER OR AN ALLOY, THE MAIN CONSTITUENT OF WHICH IS SILVER.

Dec. ,12, 1972 Filed Sept. 24. 1970 WEIGHT GAIN (fig lcm HIROAKI TAKAHASHI ETAL 3,705,796

CONTACT MATERIAL .2 Sheets-Sheet l FIG.I

THE INFLUE'NCEOFA THIRD ELEMENT,- A1 ON THE OXIDATION RATE OF Ag-29 Zn ALLOY (390C IN AIR) I Ag-3O Zn (AT v.)

Ag-29 Zn-O.88A1IAT%) l I l l TIME (HRS) Doc. 12, 1972 HIROAKI TAKAHASHI ETAL I 3,705,796

CONTACT MATERIAL Filed Sept. 24. 1970 2 Sheets-Sheet 2 FAILURE LEVEL I If Ag-29 2n o.a A1 v v [I 10 Lu I Ag m 1 Ag-29Zn-1.7I A1 F: 1 I 3 2 8 OPERATIONS DYNAMIC CONTACT RESISTANCE OF SILVER ALLOY CONTACTS OPERATED IN AIR UNDER NO LOAD CONDITION (SWITCHING CYCLEIOHZ) FAILURE LEVEL LLJ '3 10 c: Am -29 Zn 1.71 A1 I: I 3 /Ag29 Zn-O.88 A1 3 u. 1 M LLJ Z 0.1 U o i J OPERATIONS DYNAMIC CONTACT RESISTANCE OF SILVER ALLOY CONTACTS OPERATED IN AIR CONTAINING HYDROGEN-SULFIDE GASIIOOO- 2000ppm.80-87/ RH) UNDER NO LOAD cowomow (SWITCHING CYCLEI Hz) United States Patent 3,705,796 CONTACT MATERIAL Hiroaki Takahashi and Toshito Hara, Kawasaki, Japan, assignors to Fujitsu Limited, Kawasaki, Japan Filed Sept. 24, 1970, Ser. No. 75,041 Claims priority, appllisatiprlsilgpan, Sept. 29, 1969,

Int. Cl. czzc /00 US. Cl. 75-173 R 2 Claims ABSTRACT OF THE DISCLOSURE As is known, pure silver is a relatively inexpensive noble metal contact material. Moreover, oxides thereof are dissociated at a low temperature under the normal atmospheric pressure, but on the other hand, the use of pure silver as a contact material has the disadvantage that it is readily sulfurized, and contact failure occurs very easily, especially in a dry circuit.

Contact failure of the silver contact in the sulfurizing atmosphere as described above has heretofore been prevented by the alloying of the silver with a noble metal such as gold, palladium or platinum but this method makes the contact very expensive as these noble metals are expensive. Contact failure of the silver contact in the sulfurizing atmosphere can also be considerably etfectively prevented by the use of a contact material consisting of a solid solution alloy formed by adding zinc of 5-36 at to silver. This method is very advantageous from the viewpoint of the cost as zinc is readily available and inexpensive. The silver-zinc alloy contact, however, because of the ready oxidation of the zinc component, readily fails due to the formation of zinc oxide in an oxidizing atmosphere.

This invention provides an Ag-Zn-Al alloy contact material improving the oxidation resisting property greatly deteriorated by the existence of the zinc component, without deteriorating the excellent sulfurization resisting property of the Ag-Al alloy contact. This invention forms a solid solution alloy by adding aluminum to silver or a metal the main constituent of which is silver and zinc and uses this solid solution alloy as the contact material. According to this invention, the atom percentages of the Zn component and the Al component are 5-36% and 0.5- 5%, respectively, and Ag component, or the metal the main constituent of which is silver, constituting the remainder.

In the drawing:

FIG. 1 compares, graphically, the oxidation characteristic of two embodiments of the contact material according to this invention in the air at elevated temperature with the oxidation characteristic of a conventional contact material consisting of a silver-Zinc solid solution alloy under the same condition;

FIG. 2 compares, graphically, the dynamic contact characteristics of two embodiments of the contact material of the invention with the dynamic contact characteristic of a conventional contact material of pure silver in the oxidizing atmosphere; and

FIG. 3 compares the dynamic contact characteristics of two embodiments of the contact material of the invention with the dynamic contact characteristic of a conventional Patented Dec. 12, 1972 ICC contact material of pure silver in the sulfurizing atmosphere.

In further detail, FIG. 1 compares the oxidation characteristic of two embodiments of the contact material of this invention in the air of a high temperature of 390 C. with the oxidation characteristic of a conventional Ag-Zn alloy contact material in the same atmosphere. The first embodiment of this invention consists of 29 at Zn, 0.88 at Al and the remaining at Ag. The second embodiment consists of 29 at Zn, 1.71 at Al and the remaining at Ag. The conventional contact material consists of 30 at Zn, and the remaining at Ag. As evident from this figure, the addition of the Al component of the order of 2 at can effectively improve the oxidation resisting property of the Ag-Zn alloy.

FIG. 2 compares the contact characteristics of said two embodiments of the contact material of this invention used in relays in the air (switching cycle 10 Hz.) with the contact characteristic of a well known silver contact in the same atmosphere while FIG. 3 compares the contact characteristics of the same two embodiments used in relays in the air containing 1000-2000 p.p.m. hydrogen sulfide gas and -87% R.H., switching cycle 1 Hz. with the contact characteristic of the well known silver contact in the same atmosphere. No load condition was selected as the load condition as failures are most likely to occur under this condition. The contact resistance was measured under the supply voltage of 50 mv. and contact current of under 10 ma. to prevent the electrical destruction of the film in the measurement. The cumulative failure rate in the above figures is the percentage of the number of operations exceeding failure level (which is 10 in the example of FIG. 2 and 2.59 in the example of FIG. 3), divided by the number of measured operations, 80 to operations, at each measuring time. From 5 to 8 contacts were simultaneously tested under each condition. As evident from FIGS. 2 and 3, the contact material of this invention formed by adding zinc and aluminum to silver has less contact failure in the oxidizing atmosphere and the sulfurizing atmosphere compared with the conventional silver contact and is therefore a superior contact material. Addition of above 5 at aluminum will cause the increase of the contact resistance due to the oxidation or sulfurization of the aluminum component itself and as the result the contact material becomes usable. The Ag-Zn-Al alloy contact material, according to this invention, has a contact characteristic superior to that of the silver contact in both of the oxidizing atmosphere and the sulfurizing atmosphere even under a relatively large load condition that will produce arc and the contact material of this invention is an inexpensive and useful contact material that can be substituted for the silver contact.

The abbreviation at as used herein, means atoms percent.

We claim:

1. A contact material consisting essentially of 29 at zinc and 0.88-2 at aluminum, the remainder being silver.

2. The contact material of claim 1 consisting essentially of 29 at zinc, 1.71 at aluminum, the remainder being silver.

References Cited UNITED STATES PATENTS 1,863,612 6/1932 Assmann 75-l73 R L. DEWAYNE RUTLEDGE, Primary Examiner E. L. WEISE, Assistant Examiner 

